Boron nitride modified positive electrode material and preparation method thereof

Abstract

The invention discloses a boron nitride modified positive electrode material and a preparation method thereof, and belongs to the technical field of battery positive electrode materials. The boron nitride modified positive electrode comprises a current collector, and the surface of the current collector is coated with a modified positive electrode material; the modified positive electrode material comprises a binder, a conductive agent, a positive electrode material, an additive and a solvent, wherein the mass ratio of the binder to the conductive agent to the positive electrode material is (1-2): (1-2): (96-98); the additive is boron nitride, and the mass of the boron nitride is 0.2-5% of the mass of the positive electrode material. By adopting the boron nitride modified positive electrode material and the preparation method thereof, the problems of low battery capacity retention ratio, low charge-discharge efficiency and short cycle life caused by instability of the existing positive electrode material can be solved.

Description

Technical Field

[0001] The invention relates to the technical field of battery positive electrode materials, and in particular to a boron nitride modified positive electrode material and a preparation method thereof. Background Art

[0002] Improving the energy density and safety of lithium-ion batteries (LIB) has become a key issue. As the mainstream positive electrode material, nickel-rich layered oxide LiNi x Co y Mn 1-x-y O2 (NCM) and LiNi x Co y Al 1-x-y Although O2 (NCA) has high specific capacity (>200 mAh / g) and cost advantages, its inherent cycle attenuation and thermal runaway risks seriously restrict its practical application. 4+ It will trigger multiple side reactions, including: (1) lattice oxygen escape: lattice oxygen on the surface of the charged positive electrode is released in the form of O2, which reacts with the electrolyte to generate gases such as CO / CO2, resulting in a surge in interface impedance and irreversible capacity loss; (2) structural phase change: Ni in the Li layer 2+ The migration of Li induces the transformation of the layered structure into a disordered spinel / rock salt phase, hindering the + Transmission and microcrack expansion; (3) Interface corrosion: HF in the electrolyte corrodes the cathode surface, accelerates the dissolution of transition metals (Ni / Co / Mn), and destroys the stability of the solid electrolyte interface (CEI). When a short circuit occurs, Joule heat is induced to trigger the decomposition of SEI, and the heat released further promotes the exothermic reaction of the cathode-electrolyte; the lattice oxygen reacts with the electrolyte to release a large amount of heat (such as NCM811 releases 1600 J / g at 300°C); oxygen release triggers electrolyte combustion, causing the critical temperature of thermal runaway to drop below 150°C. The results show that the thermal stability of the nickel-rich cathode decreases with the increase of Ni content. LIB explosion accidents occur frequently across the country, so safety has become one of the most important issues in the field of energy storage.

[0003] Existing improvement methods include boron doping and organic additives, but they have limitations. Boron is difficult to enter the lattice and only forms a surface lithium borate layer; although organic additives (such as ITD) can construct a stable CEI, they decompose during long-term cycles. Therefore, in view of the above problems that may occur in the positive electrode during the cycle, it is necessary to develop an efficient and stable positive electrode material. Summary of the invention

[0004] The purpose of the present invention is to provide a boron nitride modified positive electrode material and a preparation method thereof, so as to solve the problems that the existing positive electrode materials are unstable, resulting in low battery capacity retention rate, low charge and discharge efficiency, and short cycle life.

[0005] To achieve the above-mentioned object, the present invention provides a boron nitride modified positive electrode, comprising a current collector, on the surface of which a modified positive electrode material is coated; the modified positive electrode material comprises a binder, a conductive agent, a positive electrode material, an additive and a solvent, wherein the mass ratio of the binder, the conductive agent and the positive electrode material is (1-2): (1-2): (96-98); the additive is boron nitride, and the mass of the boron nitride is 0.2%-5% of the mass of the positive electrode material.

[0006] Preferably, the boron nitride is boron nitride particles or boron nitride nanosheets, and the particle size of the boron nitride particles and the boron nitride nanosheets is not greater than 100 meshes.

[0007] Preferably, the binder is polyvinylidene fluoride, the conductive agent is conductive carbon black Super P, and the solvent is N-methylpyrrolidone.

[0008] Preferably, the positive electrode material is one of a lithium iron phosphate positive electrode material, a nickel-cobalt-manganese ternary oxide positive electrode material, a lithium cobalt oxide positive electrode material, and a lithium-rich manganese-based positive electrode material.

[0009] The method for preparing the boron nitride modified positive electrode comprises the following steps: S1. preparing boron nitride; S2, mixing the binder and the solvent, stirring evenly to obtain a clear colloidal solution; S3, adding the sieved boron nitride to the colloid solution, stirring evenly to obtain a mixed solution; S4, adding the conductive agent and the positive electrode material to the mixed solution and stirring evenly, adding a solvent to adjust the viscosity of the mixed solution to obtain an electrode slurry; S5. Apply the electrode slurry on the current collector, slice it and roll it after drying to obtain the positive electrode.

[0010] Preferably, the boron nitride in S1 is a boron nitride nanosheet, and the preparation method of the boron nitride nanosheet comprises the following steps: S11, mixing the boron source, the nitrogen source, the template and deionized water, and stirring to obtain a uniform solution; S12, freezing the uniform solution, and then drying it to obtain a mixed powder; S13, sintering the mixed powder to obtain boron nitride nanosheets.

[0011] Preferably, in S11, the boron source is one of borax (Na2B4O7), boric acid (H3BO3), boric anhydride (B2O3), boron halide (BCl3, BF3), borohydride (such as B2H6), the nitrogen source is one of ammonia (NH3), nitrogen (N2), urea, dicyandiamide, melamine, and ammonium chloride, the template is sodium chloride, the mass ratio of the boron source to the nitrogen source is 1:0.3~1.5, and the mass percentage of the template is 20%-80%.

[0012] Preferably, in S13, the sintering temperature is 600°C-1000°C, the heating rate is 2°C / min-30°C / min, and the holding time is 0.5h-10h.

[0013] Preferably, in S4, the viscosity of the electrode slurry is 4000cps-8000cps.

[0014] Preferably, in S5, the compaction density of the roller pressing is 3.2 g / cm 3 -3.4g / cm 3 .

[0015] The advantages and positive effects of the boron nitride modified positive electrode material and the preparation method thereof of the present invention are: 1. The present invention adds boron nitride additives to the positive electrode material. Boron nitride captures PF6 through the Lewis acid properties of boron atoms. - The stability of the electrolyte is improved; the dissolution of transition metals is inhibited by the synergistic adsorption of HF by BN; the layered structure of boron nitride nanosheets produces rapid ion transfer and low transport energy barriers, which is beneficial to the transmission of lithium ions; the stability of the positive electrode material of the soft-pack battery is improved, and the cycle life of the battery is increased.

[0016] 2. The present invention directly adds boron nitride into the slurry and adopts a coating method to prepare the positive electrode, which has a simple process and is conducive to large-scale production.

[0017] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a process flow chart of an embodiment of the present invention; Figure 2 This is a metallographic diagram of the boron nitride nanosheet of the present invention; Figure 3 A comparison chart of the capacity retention rate and charge-discharge efficiency of the soft-pack batteries assembled in Example 1 of the present invention and Comparative Example 1; Figure 4 A comparison chart of the capacity retention rate and charge-discharge efficiency of the soft-pack batteries assembled in Example 2 of the present invention and Comparative Example 2; Figure 5 It is a comparison chart of the capacity retention rate and charge and discharge efficiency of the soft-pack batteries assembled in Example 3 of the present invention and Comparative Example 3; Figure 6 A comparison chart of the capacity retention rate and charge-discharge efficiency of the soft-pack batteries assembled in Example 2, Example 4 and Comparative Example 4 of the present invention; Figure 7 This is a comparison chart of the average coulombic efficiency of the soft-pack batteries composed of Examples 1-3 of the present invention and Comparative Example 2; Figure 8 Schematic diagram of the boron nitride nanosheet channel. DETAILED DESCRIPTION

[0019] In this application, unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by technicians in the technical field of this application. In the event of any inconsistency, the meaning described in this specification or the meaning derived from the contents recorded in this specification shall prevail. In addition, the terms used herein are only for the purpose of describing the embodiments of the present application and are not intended to limit the present application. In order to accurately describe the technical content in this application and to accurately understand the present invention, the following explanations or definitions are given to the terms used in this specification before describing the specific embodiments: The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0020] A boron nitride modified positive electrode comprises a current collector, on the surface of which a modified positive electrode material is coated.

[0021] The modified positive electrode material includes a binder, a conductive agent, a positive electrode material, an additive and a solvent. The mass ratio of the binder, the conductive agent and the positive electrode material is (1-2): (1-2): (96-98). The additive is boron nitride, and the mass of the boron nitride is 0.2%-5% of the mass of the positive electrode material.

[0022] The boron nitride is boron nitride particles or boron nitride nanosheets, and the particle size of the boron nitride particles and the boron nitride nanosheets is not greater than 100 meshes.

[0023] The binder is polyvinylidene fluoride, the conductive agent is conductive carbon black Super P, and the solvent is N-methylpyrrolidone.

[0024] The positive electrode material is one of lithium iron phosphate positive electrode material, nickel cobalt manganese ternary oxide positive electrode material, lithium cobalt oxide positive electrode material and lithium-rich manganese-based positive electrode material.

[0025] like Figure 1 The method for preparing the boron nitride modified positive electrode comprises the following steps: S1. Prepare boron nitride.

[0026] The method for preparing boron nitride nanosheets comprises the following steps: S11. Mix the boron source, nitrogen source, template and deionized water, and stir evenly to obtain a uniform solution.

[0027] The boron source is one of borax (Na2B4O7), boric acid (H3BO3), boric anhydride (B2O3), boron halide (BCl3, BF3), borohydride (such as B2H6). The nitrogen source is one of ammonia (NH3), nitrogen (N2), urea, dicyandiamide, melamine, and ammonium chloride. The template is sodium chloride, and the mass ratio of the boron source to the nitrogen source is 1:0.3~1.5. The mass percentage of the template is 20%-80%.

[0028] S12, freezing the uniform solution and then drying it to obtain a mixed powder.

[0029] S13, sintering the mixed powder to obtain boron nitride nanosheets.

[0030] The sintering temperature is 600°C-1000°C, the heating rate is 2°C / min-30°C / min, and the holding time is 0.5h-10h.

[0031] The metallographic image of the prepared boron nitride nanosheets is shown in Figure 2 Boron nitride nanosheets have a two-dimensional layered structure and have excellent mechanical strength, thermal stability, oxidation resistance and chemical inertness.

[0032] S2. Mix the binder and the solvent, stir evenly, and obtain a clear colloidal solution.

[0033] S3. Sieve the boron nitride and add it to the colloid solution, stir evenly to obtain a mixed solution.

[0034] S4. Add the conductive agent and the positive electrode material to the mixed solution and stir evenly, add a solvent to adjust the viscosity of the mixed solution to obtain an electrode slurry.

[0035] The viscosity of the electrode slurry is 4000cps-8000cps.

[0036] S5. Apply the electrode slurry on the current collector, slice it and roll it after drying to obtain the positive electrode.

[0037] The compacted density of the roller is 3.2g / cm 3 -3.4g / cm 3 .

[0038] Example 1 The boron nitride modified positive electrode comprises an aluminum foil current collector, and a modified positive electrode material is coated on the surface of the current collector.

[0039] The modified positive electrode material includes polyvinylidene fluoride binder, conductive carbon black Super P, NCM811 positive electrode material, boron nitride nanosheet additive and N-methylpyrrolidone solvent.

[0040] The mass ratio of polyvinylidene fluoride, conductive carbon black Super P and NCM811 is 1.8:1.2:97.

[0041] The mass of boron nitride nanosheets is 0.2% of the mass of NCM811 positive electrode material.

[0042] The method for preparing a boron nitride modified positive electrode comprises the following steps: S1. Preparation of boron nitride nanosheets.

[0043] The method for preparing boron nitride nanosheets comprises the following steps: S11. Mix the boron source, nitrogen source, template and deionized water, and stir evenly to obtain a uniform solution.

[0044] The boron source is boric anhydride (B2O3), the nitrogen source is ammonia (NH3), and the template is sodium chloride. The mass ratio of the boron source to the nitrogen source is 1:0.5, and the mass percentage of the template is 50%.

[0045] S12, freezing the uniform solution and then drying it to obtain a mixed powder.

[0046] S13, sintering the mixed powder to obtain boron nitride nanosheets.

[0047] The sintering temperature is 600°C, the heating rate is 2°C / min, and the holding time is 1h.

[0048] S2. Mix the binder and the solvent, stir evenly, and obtain a clear colloidal solution.

[0049] S3. After sieving the boron nitride nanosheets, add them into the colloidal solution and stir them evenly to obtain a mixed solution.

[0050] S4. Add the conductive agent and the positive electrode material to the mixed solution and stir evenly, add a solvent to adjust the viscosity of the mixed solution to obtain an electrode slurry.

[0051] The viscosity of the electrode slurry was 4000 cps.

[0052] S5. Apply the electrode slurry on the current collector, slice it and roll it after drying to obtain the positive electrode.

[0053] The compacted density of the roller is 3.2g / cm 3 .

[0054] Example 2 The boron nitride modified positive electrode comprises an aluminum foil current collector, and a modified positive electrode material is coated on the surface of the current collector.

[0055] The modified positive electrode material includes polyvinylidene fluoride binder, conductive carbon black Super P, NCM811 positive electrode material, boron nitride nanosheet additive and N-methylpyrrolidone solvent.

[0056] The mass ratio of polyvinylidene fluoride, conductive carbon black Super P and NCM811 is 1.8:1.2:97.

[0057] The mass of boron nitride nanosheets is 1% of the mass of NCM811 positive electrode material.

[0058] The method for preparing a boron nitride modified positive electrode comprises the following steps: S1. Preparation of boron nitride nanosheets.

[0059] The method for preparing boron nitride nanosheets comprises the following steps: S11. Mix the boron source, nitrogen source, template and deionized water, and stir evenly to obtain a uniform solution.

[0060] The boron source is boric acid (H3BO3), the nitrogen source is dicyandiamide, and the template is sodium chloride. The mass ratio of the boron source to the nitrogen source is 1:1, and the mass percentage of the template is 60%.

[0061] S12, freezing the uniform solution and then drying it to obtain a mixed powder.

[0062] S13, sintering the mixed powder to obtain boron nitride nanosheets.

[0063] The sintering temperature is 700℃, the heating rate is 5℃ / min, and the holding time is 5h.

[0064] S2. Mix the binder and the solvent, stir evenly, and obtain a clear colloidal solution.

[0065] S3. After sieving the boron nitride nanosheets, add them into the colloidal solution and stir them evenly to obtain a mixed solution.

[0066] S4. Add the conductive agent and the positive electrode material to the mixed solution and stir evenly, add a solvent to adjust the viscosity of the mixed solution to obtain an electrode slurry.

[0067] The viscosity of the electrode slurry was 6000 cps.

[0068] S5. Apply the electrode slurry on the current collector, slice it and roll it after drying to obtain the positive electrode.

[0069] The compacted density of the roller is 3.3g / cm 3 .

[0070] Example 3 The boron nitride modified positive electrode comprises an aluminum foil current collector, and a modified positive electrode material is coated on the surface of the current collector.

[0071] The modified positive electrode material includes polyvinylidene fluoride binder, conductive carbon black Super P, NCM811 positive electrode material, boron nitride nanosheet additive and N-methylpyrrolidone solvent.

[0072] The mass ratio of polyvinylidene fluoride, conductive carbon black Super P and NCM811 is 1.8:1.2:97.

[0073] The mass of boron nitride nanosheets is 5% of the mass of NCM811 positive electrode material.

[0074] The method for preparing a boron nitride modified positive electrode comprises the following steps: S1. Preparation of boron nitride nanosheets.

[0075] The method for preparing boron nitride nanosheets comprises the following steps: S11. Mix the boron source, nitrogen source, template and deionized water, and stir evenly to obtain a uniform solution.

[0076] The boron source is borohydride (B2H6), the nitrogen source is ammonium chloride, and the template is sodium chloride. The mass ratio of the boron source to the nitrogen source is 1:1.5, and the mass percentage of the template is 80%.

[0077] S12, freezing the uniform solution and then drying it to obtain a mixed powder.

[0078] S13, sintering the mixed powder to obtain boron nitride nanosheets.

[0079] The sintering temperature is 900℃, the heating rate is 6℃ / min, and the holding time is 10h.

[0080] S2. Mix the binder and the solvent, stir evenly, and obtain a clear colloidal solution.

[0081] S3. After sieving the boron nitride nanosheets, add them into the colloidal solution and stir them evenly to obtain a mixed solution.

[0082] S4. Add the conductive agent and the positive electrode material to the mixed solution and stir evenly, add a solvent to adjust the viscosity of the mixed solution to obtain an electrode slurry.

[0083] The viscosity of the electrode slurry was 7000 cps.

[0084] S5. Apply the electrode slurry on the current collector, slice it and roll it after drying to obtain the positive electrode.

[0085] The compacted density of the roller is 3.4g / cm3 .

[0086] Example 4 The boron nitride modified positive electrode comprises an aluminum foil current collector, and a modified positive electrode material is coated on the surface of the current collector.

[0087] The modified positive electrode material includes polyvinylidene fluoride binder, conductive carbon black Super P, NCM811 positive electrode material, boron nitride particle additive and N-methylpyrrolidone solvent.

[0088] The mass ratio of polyvinylidene fluoride, conductive carbon black Super P and NCM811 is 1.8:1.2:97.

[0089] The mass of boron nitride particles is 1% of the mass of NCM811 positive electrode material.

[0090] The method for preparing a boron nitride modified positive electrode comprises the following steps: S1. Prepare boron nitride particles.

[0091] The boron nitride particles are prepared by an existing method or directly purchased.

[0092] S2. Mix the binder and the solvent, stir evenly, and obtain a clear colloidal solution.

[0093] S3. After sieving the boron nitride particles, add them into the colloid solution and stir evenly to obtain a mixed solution.

[0094] S4. Add the conductive agent and the positive electrode material to the mixed solution and stir evenly, add a solvent to adjust the viscosity of the mixed solution to obtain an electrode slurry.

[0095] The viscosity of the electrode slurry is 8000 cps.

[0096] S5. Apply the electrode slurry on the current collector, slice it and roll it after drying to obtain the positive electrode.

[0097] The compacted density of the roller is 3.4g / cm 3 .

[0098] Comparative Example 1 The difference between this comparative example and Example 1 is that the positive electrode of this comparative example does not contain any additive.

[0099] Comparative Example 2 The difference between this comparative example and Example 2 is that the positive electrode of this comparative example does not contain any additive.

[0100] Comparative Example 3 The difference between this comparative example and Example 3 is that the positive electrode of this comparative example does not contain any additive.

[0101] Comparative Example 4 The difference between this comparative example and Example 4 is that the positive electrode of this comparative example does not contain any additive.

[0102] The positive electrodes prepared in Examples 1-4 and Comparative Examples 1-4 were used to assemble NCM811||GR soft-pack batteries, and the electrolyte composition was 1M LiPF6 in DEC:DMC:EC=1:1:1 Vol%, 1%VC. The cycle performance of the soft-pack battery at a rate of 2C was studied. The NCM811||GR soft-pack battery charge and discharge test was a long cycle test at a rate of 2C constant current-constant voltage charging and 2C constant current discharge, with a voltage range of 2.8V-4.3V and a constant voltage charge / discharge cut-off current of 0.05C.

[0103] The charge and discharge efficiency and capacity retention rate of the soft-pack battery composed of Example 1 and Comparative Example 1 are as follows: Figure 3 As shown. It can be seen that the soft-pack battery of Example 1 has a higher cycle retention rate and a more stable coulombic efficiency.

[0104] The charge and discharge efficiency and capacity retention rate of the soft-pack battery composed of Example 2 and Comparative Example 2 are as follows: Figure 4 As shown, it can be seen that the soft-pack battery of Example 2 has a higher cycle retention rate and a more stable coulombic efficiency.

[0105] The charge and discharge efficiency and capacity retention rate of the soft-pack battery composed of Example 3 and Comparative Example 3 are as follows: Figure 5 As shown. It can be seen that the soft-pack battery of Example 3 has a higher cycle retention rate and a more stable coulombic efficiency.

[0106] The charge and discharge efficiency and capacity retention rate of the soft-pack batteries composed of Example 4 and Comparative Example 4 are as follows: Figure 6 As shown. It can be seen that adding boron nitride particles to the positive electrode material can improve the capacity retention rate and charge and discharge efficiency of the soft-pack battery, but the effect is lower than that of boron nitride nanosheets. The two-dimensional structure and high specific surface area of ​​boron nitride nanosheets can optimize the physical transmission path, while the surface chemical modification reduces the diffusion barrier by regulating the SEI composition and adsorption behavior, making it have better performance.

[0107] The average coulomb efficiency comparison of the soft-pack batteries composed of Examples 1-3 and Comparative Example 2 is shown in the figure Figure 7 As shown. It can be seen that the average coulombic efficiency of the soft-pack battery can be effectively improved by mixing the boron nitride nanosheets with the NCM811 positive electrode material. When the addition amount of boron nitride nanosheets is 1%, the average coulombic efficiency is the highest.

[0108] The experimental group used 1% boron nitride nanosheets as an additive, and the control group did not add boron nitride. Systematic tests were carried out on four cathode material systems: LFP, NCM811, LRM, and LCO. The other components were the same as in Example 2.

[0109] In terms of negative electrode configuration, the battery with graphite (GR) negative electrode performs a long cycle test of 2C constant current-constant voltage charging (CC-CV) and 2C constant current discharge, and the voltage window is set to 2.8-4.3 V. The lithium metal (Li) negative electrode battery adopts the test protocol of 0.1C constant current-constant voltage charging and 0.5C constant current discharge, with a voltage range of 3.0-4.3V.

[0110] The positive electrodes with different positive electrode materials were assembled into soft-pack batteries. The cycle performance of soft-pack batteries with different positive electrode materials is shown in Table 1.

[0111] Table 1 Cycling performance of soft-pack batteries with different cathode materials ;

[0112] As shown in Table 1. Compared with the control group without boron nitride, the experimental group showed a significant improvement in cycle life while maintaining the same capacity retention rate. In the LFP and NCM811 systems, the interface regulation effect of boron nitride effectively inhibited the electrode / electrolyte side reactions. In the high-voltage LCO system, the introduction of additives delays capacity decay by stabilizing the cathode-electrolyte interface phase (CEI). For the lithium metal negative electrode system, the mechanical reinforcement effect and lithium ion flux regulation function of boron nitride further optimize the lithium deposition behavior.

[0113] Analysis of the protective mechanism of boron nitride on the positive electrode 1. Boron nitride's dual protection mechanism improves electrode stability The formation of Li2CO3 as cathode-electrolyte interface (CEI) originates from the oxidative decomposition of carbonate-based electrolytes. In the presence of LiPF6, its oxidative stability is significantly reduced, resulting in the formation of Ni 4+ Irreversible reduction to Ni 2+ , and triggers spinel / rock salt phase reconstruction and HF (Formula I) corrosion (originating from the hydrolysis of LiPF6 (Formula II)), resulting in capacity decay.

[0114] ; ;

[0115] In view of the interface degradation problem of traditional NCM cathode, h-BN achieves breakthrough improvement through the following synergistic effects: 1. The Lewis acid properties of boron atoms capture PF6 - and improve electrolyte stability; The boron atoms in h-BN are in an electron-deficient state due to their low electronegativity and can act as Lewis acid sites, preferentially reacting with PF6 - anion binding. This adsorption reduces PF6 - The decomposition of h-BN can inhibit the oxidative decomposition of carbonate-based electrolytes at high voltages. At the same time, the introduction of h-BN improves the overall oxidation stability of the electrolyte by strongly binding boron atoms to lithium salts. This process reduces interfacial side reactions, reduces the formation of the CEI layer, and alleviates the surface Ni 2+ The generation of ions ultimately increases the degree of lithium ion in the electrode under full discharge state.

[0116] 2. BN synergistically adsorbs HF and inhibits transition metal dissolution; The boron atoms (Lewis acid) and nitrogen atoms (Lewis base) of h-BN can adsorb HF molecules through their electron-deficient and electron-rich properties, respectively. Boron atoms capture H in HF through electrostatic interaction. + , while nitrogen atoms interact with F through their lone pair electrons - Combined, they jointly reduce HF corrosion on the electrode. In addition, this synergistic effect also reduces the surface Ni 2+ The exposure inhibits the dissolution of transition metals (such as Ni, Co, and Mn).

[0117] 3. Synergy and performance improvement The synergistic effect of the above two mechanisms reduces the side reactions and structural degradation at the electrode / electrolyte interface. The partial ionic characteristics of the BN bond of h-BN make it both chemically stable and surface reactive, which can stabilize the electrolyte and adsorb harmful substances. These effects jointly improve the cycle stability and capacity retention of NCM materials.

[0118] 2. Multi-scale synergistic enhancement of lithium ion transport kinetics Boron nitride (BN) materials (including powder particles and nanosheets) achieve efficient lithium ion transport through interface coupling-induced directional transport: the empty pz orbitals of boron atoms on the BN surface are induced by Li + The electron affinity of BN (binding energy of about -2.3 eV) makes it have a strong charge-dipole interaction with lithium ions. This coupling effect causes a local high concentration of Li + The adsorption layer (density can reach 3 times that of the bulk electrolyte) guides the ions to migrate along the (002) crystal plane through the gradient electric field of the polar BN bonds.

[0119] Boron nitride particles are usually formed by disordered stacking of multiple h-BN sheets, which are bonded by van der Waals forces and have random stacking angles (such as ABC or ABA mode), resulting in high structural tortuosity and a diffusion barrier of 0.5 eV. Nitrogen vacancies, boron vacancies or grain boundary defects are easily present on the particle surface and between layers, and the vacancy density can reach 1010 / cm 2 , affecting the continuity of the lithium ion transmission path.

[0120] like Figure 8 As shown. The layered structure of the boron nitride nanosheets (interlayer spacing 0.333 nm) forms a size matching effect with the diameter of lithium ions (0.152 nm). Parallel layer direction: Li + Slip along the honeycomb channel formed by the BN hexacyclic ring, a low-curvature channel in the plane, and a migration barrier as low as 0.07 eV; vertical layer direction: defects such as nitrogen vacancies can form local channels (about 0.5-1nm in size), allowing Li + Crossing the interlayer potential barrier, a three-dimensional percolation network is formed, resulting in fast ion transfer and low transport energy barrier.

[0121] Therefore, the boron nitride modified positive electrode material and the preparation method thereof described in the present invention can solve the problem that the existing positive electrode material is unstable, resulting in low battery capacity retention rate, low charge and discharge efficiency, and short cycle life.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A boron nitride modified positive electrode, characterized in that: The invention comprises a current collector, on the surface of which a modified positive electrode material is coated; the modified positive electrode material comprises a binder, a conductive agent, a positive electrode material, an additive and a solvent, wherein the mass ratio of the binder, the conductive agent and the positive electrode material is (1-2):(1-2):(96-98); the additive is boron nitride, and the mass of the boron nitride is 0.2%-5% of the mass of the positive electrode material.

2. A boron nitride modified positive electrode according to claim 1, characterized in that: The boron nitride is boron nitride particles or boron nitride nanosheets, and the particle size of the boron nitride particles and the boron nitride nanosheets is not greater than 100 meshes.

3. A boron nitride modified positive electrode according to claim 1, characterized in that: The binder is polyvinylidene fluoride, the conductive agent is conductive carbon black Super P, and the solvent is N-methylpyrrolidone.

4. A boron nitride modified positive electrode according to claim 1, characterized in that: The positive electrode material is one of a lithium iron phosphate positive electrode material, a nickel-cobalt-manganese ternary oxide positive electrode material, a lithium cobalt oxide positive electrode material, and a lithium-rich manganese-based positive electrode material.

5. A method for preparing a boron nitride modified positive electrode as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: S1. preparing boron nitride; S2, mixing the binder and the solvent, stirring evenly to obtain a clear colloidal solution; S3, adding the sieved boron nitride to the colloid solution, stirring evenly to obtain a mixed solution; S4, adding the conductive agent and the positive electrode material to the mixed solution and stirring evenly, adding a solvent to adjust the viscosity of the mixed solution to obtain an electrode slurry; S5. Apply the electrode slurry on the current collector, slice it and roll it after drying to obtain the positive electrode.

6. The method for preparing a boron nitride modified positive electrode according to claim 5, characterized in that: The boron nitride in S1 is a boron nitride nanosheet, and the preparation method of the boron nitride nanosheet comprises the following steps: S11, mixing the boron source, the nitrogen source, the template and deionized water, and stirring to obtain a uniform solution; S12, freezing the uniform solution, and then drying it to obtain a mixed powder; S13, sintering the mixed powder to obtain boron nitride nanosheets.

7. The method for preparing a boron nitride modified positive electrode according to claim 6, characterized in that: In the S11, the boron source is one of borax, boric acid, boric anhydride, boron halide, and borohydride, the nitrogen source is one of ammonia, nitrogen, urea, dicyandiamide, melamine, and ammonium chloride, the template is sodium chloride, the mass ratio of the boron source to the nitrogen source is 1:0.3-1.5, and the mass percentage of the template is 20%-80%.

8. The method for preparing a boron nitride modified positive electrode according to claim 6, characterized in that: In S13, the sintering temperature is 600°C-1000°C, the heating rate is 2°C / min-30°C / min, and the holding time is 0.5h-10h.

9. The method for preparing a boron nitride modified positive electrode according to claim 5, characterized in that: In the above-mentioned S4, the viscosity of the electrode slurry is 4000cps-8000cps.

10. The method for preparing a boron nitride modified positive electrode according to claim 5, characterized in that: In S5, the compaction density of the roller pressing is 3.2 g / cm 3 -3.4g / cm 3 .

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